The present invention relates generally to a current reference circuit, and more particularly, to a switched capacitor current reference circuit with low dependence on process, voltage and temperature.
A current reference circuit used to bias various circuit modules such as op-amps, comparators, data converter bias circuits, and phase-lock loops is an important building block in analog and mixed-signal integrated circuits. Such circuit modules require a precise current reference with low dependence on Process, Voltage, and Temperature (PVT). One method of generating a precise current reference is with a voltage to current converter circuit in which either a stable external reference voltage or a band-gap reference voltage is applied across an external resistor. This method requires that the value of the external resistor must remain almost constant under different operating conditions. Integrated resistors have a large spread across PVT and consume a large silicon area and therefore, are less than ideal for generating a precise current reference. Using an off-chip voltage reference and external resistor for a current reference generator increases the chip pin count and the number of board components. The use of an on-chip band-gap reference circuit also requires a separate V to I converter with an external resistor, and requires the use of at least two op-amps, one for a band-gap circuit and another for V to I conversion.
Accordingly, it would be advantageous to have a current reference circuit for generating a substantially constant current independent of PVT, and which circuit may be formed on an integrated circuit.